1. Field of the Invention
The present invention relates to an engine control system and, more particularly, a control system for an internal combustion automotive engine equipped with two air-fuel ratio feedback control systems for controlling fuel injection rates for two groups of fuel injectors independently.
2. Description of Related Art
Some internal combustion engines are equipped with two air-fuel ratio feedback control systems. Such internal combustion engines, which typically are V-type internal combustion engines, are usually provided with one air-fuel ratio sensor in the exhaust system for each of a pair of cylinder banks. The air-fuel ratio for cylinders of each bank is controlled by a signal from another air-fuel ratio sensor. Such an automotive engine control system is known from, for instance, Japanese Unexamined Patent Publication No. 1-177,435.
In such a V-type internal combustion engine, it is common to provide an air flow meter for detecting the air flow rate of intake air in an air intake passage common to both of the cylinder banks. A basic injection rate of fuel is established for an injector of each bank on the basis of an air flow rate detected by the air flow meter. A feedback correction value relating to the basic injection rate for the injector of each cylinder bank is determined from the air-fuel ratio detected by the air-fuel ratio sensor of the bank.
A control system of this type, however, may have a problem in that the intake air flow meter may incorrectly determine intake air flow rates due, for example, to deterioration with time or to aging. As a result, the basic injection rate of the fuel itself, which is established on the basis of an incorrectly determined intake air flow rate, is incorrect, and the air-fuel ratio feedback control system is subjected to large demands in order to compensate for the incorrectly determined intake air flow rate.